Lucy & Edward secretly write to each other and have exchanged gifts. I doubt they use each other’s Christian names or have been touchy-feely in public because they want the engagement to remain a secret unlike Marianne & Willoughby who are not engaged but act to the world as if they are. I think secret engagements were considered disrespectful to family and friends by leaving the family out of the process of such an important decision and by keeping it secret the couple is never on an equal level of frankness with anyone. Jane Fairfax has much guilt for keeping her engagement a secret telling Emma "You are very kind, but I know what my manners were to you. So cold and artificial! I had always a part to act. It was a life of deceit! I know that I must have disgusted you." (E, Ch. 52) I think Edward feels this type of guilt very deeply and especially after Marianne pronounces him reserved in Ch. 17. Secret engagements I think might also be made in haste without appropriate thought. It seems to me Edward has made a terrible mistake proposing to Lucy. According to Elinor’s observations they do not seem compatible and I do not feel Lucy’s rosy description of their relationship is an honest one. Edward seems miserable and if Elinor is correct he has fallen in love with her and presumably is no longer in love with Lucy. Poor man, he appears to be honoring his engagement.